This invention relates to flame retardant or self-extinguishing crosslinked polymer compositions which contain a normally flammable and/or poorly flame retardant crosslinked olefin polymer, elemental phosphorus and halogenated organic moiety.
By reason of their favorable physical properties and relatively low cost, olefin polymers have been used for most widely diverse applications including applications as solid molding materials and as foamed compositions.
For many applications, however, plastic materials having heat resistances generally higher than those possessed by typical olefin polymers are required. Accordingly, it has been a practice to employed various crosslinking means such as irradiation, chemical crosslinking agents, heat and combinations thereof in the fabrication of olefin polymers in order to increase their heat resistance. The resultant crosslinked polymers are useful in the fabrication of heat resistant solid and formed articles.
In recent times, it has become increasingly important to impart flame resistant properties to such olefin polymers. This is particularly true where solid olefin polymers are used as insulating material in the electrical industry and where foamed olefin polymers are used as insulation and to prevent risk of fire in the daily use of other items.
It has been proposed heretofore to impart flame-retardancy to an olefin polymer by incorporating various additives into the polymer. Flame-retardance has been obtained, for instance, by combining with the polymer a solid chlorinated hydrocarbon, e.g., chlorinated paraffin, with a flame-retardant inorganic oxide, preferably antimony oxide, in critical proportions to each other and to the polymer. Such compositions are described in U.S. Pats. Nos. 2,480,298, 2,590,211 and 2,669,521.
Unfortunately, in many crosslinked olefin polymers, very substantial amounts of such additives must be employed in order to obtain a polymer having suitable fire-retardance. In addition, antimony oxide is a potential environmental pollutant. Also, polymers containing such large amounts of additive often require additional radiation or other crosslinking means in order to achieve the desired degree of crosslinking.
In view of these disadvantages it would be highly desirable to provide a more economical and less toxic means for rendering crosslinked olefin polymers flame-retardant or self-extinguishing.